The present disclosure relates to implantable medical devices and, more particularly, systems and methods that permit a titanium or titanium alloy part and a ceramic part to be brazed together to achieve a hermetic seal.
Body implanted devices are generally hermetically sealed to keep fluids and water vapor from infiltrating into the device and destroying the electronic circuitry contained within the device. Typically, the medical device has an outer housing that is made of a biocompatible material such as a ceramic or a metal.
While a medical device housing may be made almost entirely of a biocompatible metal such as titanium, it may be necessary for example, in some medical applications to have a housing which is made substantially from a non-metallic material because a receiving/transmitting antenna may be included inside the housing. Such an antenna may not be operable within a housing that is completely made from metal, e.g., titanium, since metal can effectively act as a shield against RF energy transmissions.
One such application where it is often, for example, to have a composite device housing consisting of a non-metal material, e.g., a ceramic, and a metal, e.g., titanium, is an implantable microstimulator. A microstimulator has very small dimensions and can have metal electrode contacts integrated into the housing. The small dimensions allow a microstimulator to be implanted with less surgical trauma compared to a larger, implantable stimulator device.
Because of the small size of a microstimulator, it generally does not use a primary (one-time-use-only) battery but uses, instead, a replenishable power source such as a rechargeable battery. The rechargeable battery, contained in the microstimulator, is charged inductively with transcutaneous RF power transmissions. In addition, the RF transmissions may also be used to transfer data and commands between the implanted device and the external device that is connected to the secondary antenna. Such RF power/data transmissions require the use of a primary, internal antenna that may be placed inside the device housing and a secondary, external antenna that is not implanted. In order to achieve effective and efficient RF power transmissions through the stimulator housing, the housing can be made at least partly of a non-metallic material. The use of a housing that is at least partly non-metallic can improve the magnetic inductance between the internal antenna within or on the implantable device and an external antenna.
An example microstimulator that employs a rechargeable battery and derives power from transcutaneous RF power transmissions is a BION® implantable microstimulator, manufactured by Advanced Bionics® Corporation, Valencia, Calif.
The following list of applications, publications and patents, which are all herein incorporated by reference, describe various details associated with the manufacture, operation and use of BION implantable microstimulators.
Application/Filing/Patent/PublicationPublication No.DateTitleU.S. Pat. No. IssuedImplantable Microstimulator5,193,539Mar. 16, 1993U.S. Pat. No. IssuedStructure and Method of 5,193,540Mar. 16, 1993Manufacture of an Implantable MicrostimulatorU.S. Pat. No. IssuedImplantable Device Having an 5,312,439May 17, 1994Electrolytic Storage ElectrodeU.S. Pat. No. IssuedImplantable Microstimulator5,324,316Jun. 28, 1994U.S. Pat. No. IssuedStructure and Method of 5,405,367Apr. 11, 1995Manufacture of an Implantable MicrostimulatorPCT PublicationPublishedBattery-Powered Patient WO 98/37926Sep. 3, 1998Implantable DevicePCT PublicationPublishedSystem of Implantable Devices WO 98/43700Oct. 8, 1998For Monitoring and/orAffecting Body ParametersPCT PublicationPublishedSystem of Implantable Devices WO 98/43701Oct. 8, 1998For Monitoring and/orAffecting Body ParametersU.S. Pat. No. IssuedImproved Implantable 6,051,017Apr. 18, 2000Microstimulator and SystemsEmploying SamePublishedMicromodular Implants to September, 1997Provide Electrical Stimulationof Paralyzed Muscles and Limbs, by Cameron, et al., published inIEEE Transactions on BiomedicalEngineering, Vol. 44, No. 9, pages 781-790.
The BION microstimulator has a small housing that may be partly metal, e.g., titanium and partly non-metallic, e.g., a ceramic. Because the microstimulator uses a rechargeable battery and contains an antenna for receiving power and/or data transmissions, it may be necessary for example, for at least a part of the housing to be non-metallic. In addition, because the microstimulator has both anode and cathode electrode contacts, which are typically both metals, it may be necessary for example, to hermetically seal the interface between the metal electrode contacts and the non-metallic, e.g., ceramic part of the housing. Thus, the housing may comprise a metal part and a non-metallic part, which two parts exhibit different mechanical properties. The construction of such a composite housing for a microstimulator is challenging because: (1) the two dissimilar materials, ceramic and titanium have different mechanical properties, including thermal coefficients of expansions and (2) the method of joining for example, must yield a strong, hermetic seal.
Nickel has been used to create a brazed interface. U.S. Pat. No. 6,521,350 to Fey et al. employs an interlayer of pure nickel to form a bond between a ceramic part and a titanium part. U.S. Pat. No. 6,221,513 to Lasater uses a titanium nickel (Ti—Ni) alloy as interface material between ceramic and titanium. Both patents are herein incorporated by reference in their entireties.
A need exists for alternative systems and methods for hermetically sealing a medical device housing that may be partly ceramic and partly titanium.